The disclosures of Japanese Patent Application Nos. HEI 11-312707 filed on Nov. 2, 1999 and 2000-137881 filed on May 10, 2000, including the specifications, drawings and abstracts are incorporated herein by reference in their entirety.
1. Field of the Invention
The present invention relates to an apparatus and a method for diagnosing an abnormality in a fuel vapor purge system that purges fuel vapor that has been evaporated from a fuel tank and has been adsorbed to a canister into an intake passage of an internal combustion engine. More particularly, the invention relates to an abnormality diagnostic apparatus and method of a fuel vapor purge system that has a changing means for changing a communication passage connecting the fuel tank and the intake passage between a main passage in communication with the canister and a bypass passage that bypasses the canister.
2. Description of the Related Art
A known fuel vapor process apparatus that purges fuel vapor occurring in a fuel tank into an intake passage to prevent emission of fuel vapor from the fuel tank into the atmosphere is disclosed in, for example, Japanese Patent Application Laid-Open No. HEI 10-184464. The fuel tank has a deformable partition film that separates an internal space of the fuel tank into a fuel chamber and an air chamber in a tightly closed fashion in order to reduce occurrence of fuel vapor. The fuel vapor process apparatus has a canister for adsorbing fuel vapor from the fuel tank, and a purge control valve for controlling the open/close state between the canister and the intake passage. When the purge control valve of this apparatus is opened during operation of the internal combustion engine, negative pressure from the intake passage is introduced into the canister. In this case, therefore, air flows from the fuel tank toward the intake passage, so that fuel adsorbed in the canister is purged toward the intake passage. Hence, the above-described fuel vapor process apparatus is able to supply fuel vapor occurring in the fuel tank into the intake passage of the engine as a fuel without letting it out into the atmosphere.
However, if a hole is formed in the partition film of the fuel tank, fuel leaks into the air chamber, so that a portion of the fuel vapor may escape into the atmosphere. Therefore, in the fuel tank equipped with the partition film, it is necessary to detect whether the partition film has a hole.
The concentration of fuel vapor in the air chamber is low when the partition film has no hole. If a hole is formed in the partition film, the fuel vapor concentration in the air chamber increases. Therefore, as a technique for diagnosing whether the partition film has a hole, it is conceivable to stop purging fuel from the canister into the intake passage, and purge gas from the air chamber directly into the intake passage, and detect the concentration of gas occurring at the time of purge from the air chamber (hereinafter, referred to as xe2x80x9cvapor concentrationxe2x80x9d). By this technique, it becomes possible to determine that the partition film has a hole if the vapor concentration is relatively high, and to determine that the partition film has no hole if the vapor concentration is relatively low.
If the aforementioned technique is used to determine whether the partition film has a hole, it is necessary to provide a bypass passage between the fuel tank and the intake passage for bypassing the canister, and a change valve that changes between a state of communication between the fuel tank and the intake passage via the canister and a state of communication therebetween via the bypass passage. Hereinafter, the bypass passage and the change valve may be collectively referred to as xe2x80x9cbypass systemxe2x80x9d if necessary.
In the above-described construction, however, if the change valve is held in either one of the states for a long time, carbon likely deposits on and around movable portions of the change valve, so that the bypass passage may suffer a clogged abnormality, or a fixation abnormality in which the change valve cannot change the state of communication. If such an abnormality occurs in the bypass system, gas is not properly purged from the fuel tank into the intake passage, so that it becomes impossible to precisely detect whether there is a hole in the partition film. Therefore, in the above-described construction, it is necessary to determine whether the bypass system has an abnormality.
It is an object of the invention to provide an abnormality diagnostic apparatus and method of a fuel vapor purge system that is capable of determining whether the bypass system has an abnormality.
An abnormality diagnostic apparatus of a fuel vapor purge system in accordance with a first aspect of the invention includes a fuel tank connectable in communication to the atmosphere, a main passage connecting the fuel tank and an intake passage of an internal combustion engine via a canister for adsorbing a fuel vapor from the fuel tank, a bypass passage connecting the fuel tank and the intake passage, bypassing the canister, changing means for selectively changing a communication passage between the fuel tank and the intake passage between the main passage and the bypass passage, pressure detecting means for detecting a pressure in the fuel tank, and abnormality determining means for determining whether there is an abnormality in at least one of the bypass passage and the changing means based on the pressure detected by the pressure detecting means before and after an operation of changing between the main passage and the bypass passage is performed while air is flowing from the fuel tank toward the intake passage.
In this aspect, the flow passage resistance to gas differs between when gas from the fuel tank flows toward the intake passage through the canister and when gas from the fuel tank flows toward the intake passage, bypassing the canister. Since the fuel tank communicates with the atmosphere, the internal pressure in the fuel tank converges to a value close to the atmospheric pressure if the flow passage resistance to gas flowing from the fuel tank to the intake passage is great. If that flow passage resistance is small, the internal pressure in the fuel tank converges to a value that is remote from the atmospheric pressure.
If the bypass passage is clogged under a condition that the fuel tank and the intake passage are connected in communication via the bypass passage, the flow passage resistance becomes great, so that the internal pressure in the fuel tank converges to a value near the atmospheric pressure. If the changing means has an abnormality, the internal pressure in the fuel tank hardly changes before and after the operation of changing the communication passage is performed by the changing means. Conversely, if neither the bypass passage nor the changing means has an abnormality, the internal pressure in the fuel tank converges to one of two different values that corresponds to the currently selected passage, because the bypass passage and the main passage have different flow passage resistances. Therefore, by detecting the pressures in the fuel tank before and after the operation of changing the communication passage is performed by the changing means in a condition where air is flowing from the fuel tank to the intake passage, it becomes possible to determine whether there is an abnormality in the bypass passage or the changing means.
An abnormality diagnostic apparatus of a fuel vapor purge system in accordance with a second aspect of the invention includes a fuel tank connectable in communication to an atmosphere, a main passage connecting the fuel tank and an intake passage of an internal combustion engine via a canister for adsorbing a fuel vapor from the fuel tank, a bypass passage connecting the fuel tank and the intake passage, bypassing the canister, changing means for selectively changing a communication passage between the fuel tank and the intake passage between the main passage and the bypass passage, pressure detecting means for detecting a pressure in the bypass passage, and abnormality determining means for determining whether there is an abnormality in at least one of the bypass passage and the changing means based on the pressure detected by the pressure detecting means before and after an operation of changing the communication passage is performed by the pressure detecting means while air is flowing from the fuel tank toward the intake passage.
In this aspect, the flow passage resistance to gas differs between when gas flows from the fuel tank toward the intake passage through the canister and when gas flows from the fuel tank toward the intake passage bypassing the canister. In this case, while air is flowing from the fuel tank toward the intake passage, the internal pressure in the bypass passage converges to different values. Therefore, by detecting the pressures occurring in the bypass passage before and after the operation of changing the communication passage is performed by the changing means in a condition where air is flowing from the fuel tank toward the intake passage, it becomes possible to determine whether there is an abnormality in the bypass passage or the changing means.
If the amount of flow of air from the fuel tank to the intake passage becomes small, that is, the flow rate of air becomes low, after the operation of changing the communication passage is performed by the changing means, the internal pressure in the fuel tank or the internal pressure in the bypass passage becomes a value near the atmospheric pressure. In this case, the difference between the flow passage resistance of the main passage and the flow passage resistance of the bypass passage does not remarkably appear in the aforementioned internal pressure. Therefore, if it is determined whether the bypass passage or the changing means has an abnormality based on the internal pressure under a condition that the amount of flow of air from the fuel tank to the intake passage is small, it becomes impossible to clearly discriminate whether the internal pressure is attributed to a reduction in the amount of flow of air or to an abnormality in the bypass passage or the changing means, so that such an abnormality cannot be accurately determined. Therefore, in order to accurately determine whether the bypass passage or the changing means has an abnormality, it is appropriate to determine whether the bypass passage or the changing means has an abnormality based on the aforementioned internal pressure under a condition where the difference between the flow passage resistance of the main passage and the flow passage resistance of the bypass passage can reliably appear, for example, a condition where the amount of flow of air from the fuel tank to the intake passage is at least a predetermined value continues for a relatively long time, etc., after the operation of changing the communication passage is performed by the changing means.
In the first and second aspects, the abnormality determining means may determine whether there is an abnormality in at least one of the bypass passage and the changing means based on the pressure detected by the pressure detecting means under a condition where a difference between a flow passage resistance of the main passage and a flow passage resistance of the bypass passage is allowed to appear, after the operation of changing the communication passage is performed by the changing means. Therefore, the precision in determination regarding the abnormality can be improved.
In the aforementioned aspects, the abnormality determining means may determine whether there is an abnormality in at least one of the bypass passage and the changing means based on the pressure detected by the pressure detecting means at a time point when a state where an amount of flow of air from the fuel tank to the intake passage is at least a predetermined value continues for a predetermined length of time after the operation of changing the communication passage is performed by the changing means.
Furthermore, in the aforementioned aspects, the abnormality determining means may determine whether there is an abnormality in at least one of the bypass passage and the changing means based on whether there is a period during which an absolute value of an amount of change in the pressure detected by the pressure detecting means becomes at least a predetermined amount while a state where an amount of flow of air from the fuel tank to the intake passage is at least a predetermined value continues for a predetermined length of time after the operation of changing the communication passage is performed by the changing means.
If the bypass passage is clogged under a condition where the fuel tank and the intake passage are connected in communication via the bypass passage, the flow passage resistance becomes large, and the internal pressure in the fuel tank converges to a value close to the atmospheric pressure, as mentioned above.
Therefore, in the first and second aspects, the abnormality determining means may determine that the bypass passage has a clogged abnormality if the pressure detected by the pressure detecting means becomes substantially equal to an atmospheric pressure after the communication passage is changed to the bypass passage by the changing means.
If the changing means has an abnormality, the internal pressure in the fuel tank hardly changes before and after the operation of changing the communication passage is performed by the changing means.
Therefore, in the first and second aspects, the abnormality determining means may determine that the changing means has an abnormality if an absolute value of an amount of change from the pressure detected by the pressure detecting means before the operation of changing the communication passage is performed by the changing means to the pressure detected by the pressure detecting means after the operation of changing the communication passage is performed is at most a predetermined value.
Furthermore, in the first and second aspects, the abnormality diagnostic apparatus may determine whether there is an abnormality in at least one of the bypass passage and the changing means based on an extent of variation of the pressure detected by the pressure detecting means before and after the operation of changing the communication passage is performed by the changing means.
In the aforementioned aspects, the extent of variation of the internal pressure in the fuel tank and the extent of variation of the internal pressure in the bypass passage differ from each other because the flow passage resistance differs between when gas is flowing from the fuel tank toward the intake passage through the canister and when gas flows toward the intake passage, bypassing the canister.
If the bypass passage is clogged, the internal pressure in the fuel tank and the internal pressure in the bypass passage hardly vary but remain at fixed values. If the changing means has an abnormality, the extent of variation of the internal pressure in the fuel tank and the extent of variation of the internal pressure in the bypass passage hardly change before and after the operation of changing the communication passage is performed by the changing means. If both the bypass passage and the changing means are normally functioning, the extent of variation of the internal pressure in the fuel tank and the extent of variation of the internal pressure in the bypass passage change before and after the passage change by the changing means. Therefore, by detecting the extent of vibration of the internal pressure in the fuel tank or the extent of vibration of the internal pressure in the bypass passage before and after the operation of changing the communication passage is performed by the changing means while air is flowing from the fuel tank to the intake passage, it becomes possible to determine whether the bypass passage or the changing means has an abnormality.
At the time of a fluctuation in the operational state of the internal combustion engine or the like, the negative pressure led into the intake passage also fluctuates, so that the amount of flow of air from the fuel tank toward the intake passage changes, and therefore the value of convergence of the internal pressure in the fuel tank or the internal pressure in the bypass passage fluctuates. If under such a condition, it is determined whether the bypass passage or the changing means has an abnormality based on the aforementioned internal pressures occurring before and after the operation of changing the communication passage is performed by the changing means, it becomes impossible to clearly discriminate whether the fluctuation in the internal pressure is caused by a change in the amount of flow of air or by an abnormality in the bypass passage or the changing means, so that it becomes impossible to accurately determine whether the bypass passage or the changing means has an abnormality.
If a predetermined operational state of the internal combustion engine is maintained, the negative pressure led into the intake passage does not fluctuate, so that the amount of flow of air from the fuel tank to the intake passage does not change. In this case, the internal pressure in the fuel tank or the bypass passage converges to a constant value corresponding to the flow passage resistance between the fuel tank and the intake passage.
Therefore, in the first and second aspects, if a predetermined operational state of the internal combustion engine is maintained when it is determined by the abnormality determining means whether the bypass passage or the changing means has an abnormality, it becomes possible to improve the precision in determination regarding an abnormality in the bypass passage or the changing means.